/*
 * Copyright 2001-2004 Unicode, Inc.
 *
 * Disclaimer
 *
 * This source code is provided as is by Unicode, Inc. No claims are
 * made as to fitness for any particular purpose. No warranties of any
 * kind are expressed or implied. The recipient agrees to determine
 * applicability of information provided. If this file has been
 * purchased on magnetic or optical media from Unicode, Inc., the
 * sole remedy for any claim will be exchange of defective media
 * within 90 days of receipt.
 *
 * Limitations on Rights to Redistribute This Code
 *
 * Unicode, Inc. hereby grants the right to freely use the information
 * supplied in this file in the creation of products supporting the
 * Unicode Standard, and to make copies of this file in any form
 * for internal or external distribution as long as this notice
 * remains attached.
 */

/* ---------------------------------------------------------------------

	Conversions between UTF32, UTF-16, and UTF-8. Source code file.
	Author: Mark E. Davis, 1994.
	Rev History: Rick McGowan, fixes & updates May 2001.
	Sept 2001: fixed const & error conditions per
	mods suggested by S. Parent & A. Lillich.
	June 2002: Tim Dodd added detection and handling of incomplete
	source sequences, enhanced error detection, added casts
	to eliminate compiler warnings.
	July 2003: slight mods to back out aggressive FFFE detection.
	Jan 2004: updated switches in from-UTF8 conversions.
	Oct 2004: updated to use UNI_MAX_LEGAL_UTF32 in UTF-32 conversions.

	See the header file "ConvertUTF.h" for complete documentation.

	------------------------------------------------------------------------ */

#include "behaviac/common/convertutf.h"
#ifdef CVTUTF_DEBUG
#include <stdio.h>
#endif

static const int halfShift = 10; /* used for shifting by 10 bits */

static const UTF32 halfBase = 0x0010000UL;
static const UTF32 halfMask = 0x3FFUL;

#define UNI_SUR_HIGH_START  (UTF32)0xD800
#define UNI_SUR_HIGH_END    (UTF32)0xDBFF
#define UNI_SUR_LOW_START   (UTF32)0xDC00
#define UNI_SUR_LOW_END     (UTF32)0xDFFF

#ifndef false
#define false	   0
#endif

#ifndef true
#define true	    1
#endif

namespace behaviac {
    /* --------------------------------------------------------------------- */

    ConversionResult ConvertUTF32toUTF16(
        const UTF32** sourceStart, const UTF32* sourceEnd,
        UTF16** targetStart, UTF16* targetEnd, ConversionFlags flags) {
        ConversionResult result = conversionOK;
        const UTF32* source = *sourceStart;
        UTF16* target = *targetStart;

        while (source < sourceEnd) {
            UTF32 ch;

            if (target >= targetEnd) {
                result = targetExhausted;
                break;
            }

            ch = *source++;

            if (ch <= UNI_MAX_BMP) { /* Target is a character <= 0xFFFF */
                /* UTF-16 surrogate values are illegal in UTF-32; 0xffff or 0xfffe are both reserved values */
                if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                    if (flags == strictConversion) {
                        --source; /* return to the illegal value itself */
                        result = sourceIllegal;
                        break;

                    } else {
                        *target++ = UNI_REPLACEMENT_CHAR;
                    }
                } else {
                    *target++ = (UTF16)ch; /* normal case */
                }
            } else if (ch > UNI_MAX_LEGAL_UTF32) {
                if (flags == strictConversion) {
                    result = sourceIllegal;

                } else {
                    *target++ = UNI_REPLACEMENT_CHAR;
                }
            } else {
                /* target is a character in range 0xFFFF - 0x10FFFF. */
                if (target + 1 >= targetEnd) {
                    --source; /* Back up source pointer! */
                    result = targetExhausted;
                    break;
                }

                ch -= halfBase;
                *target++ = (UTF16)((ch >> halfShift) + UNI_SUR_HIGH_START);
                *target++ = (UTF16)((ch & halfMask) + UNI_SUR_LOW_START);
            }
        }

        *sourceStart = source;
        *targetStart = target;
        return result;
    }

    /* --------------------------------------------------------------------- */

    ConversionResult ConvertUTF16toUTF32(
        const UTF16** sourceStart, const UTF16* sourceEnd,
        UTF32** targetStart, UTF32* targetEnd, ConversionFlags flags) {
        ConversionResult result = conversionOK;
        const UTF16* source = *sourceStart;
        UTF32* target = *targetStart;
        UTF32 ch, ch2;

        while (source < sourceEnd) {
            const UTF16* oldSource = source; /*  In case we have to back up because of target overflow. */
            ch = *source++;

            /* If we have a surrogate pair, convert to UTF32 first. */
            if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END) {
                /* If the 16 bits following the high surrogate are in the source buffer... */
                if (source < sourceEnd) {
                    ch2 = *source;

                    /* If it's a low surrogate, convert to UTF32. */
                    if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END) {
                        ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
                             + (ch2 - UNI_SUR_LOW_START) + halfBase;
                        ++source;

                    } else if (flags == strictConversion) { /* it's an unpaired high surrogate */
                        --source; /* return to the illegal value itself */
                        result = sourceIllegal;
                        break;
                    }
                } else { /* We don't have the 16 bits following the high surrogate. */
                    --source; /* return to the high surrogate */
                    result = sourceExhausted;
                    break;
                }
            } else if (flags == strictConversion) {
                /* UTF-16 surrogate values are illegal in UTF-32 */
                if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END) {
                    --source; /* return to the illegal value itself */
                    result = sourceIllegal;
                    break;
                }
            }

            if (target >= targetEnd) {
                source = oldSource; /* Back up source pointer! */
                result = targetExhausted;
                break;
            }

            *target++ = ch;
        }

        *sourceStart = source;
        *targetStart = target;
#ifdef CVTUTF_DEBUG

        if (result == sourceIllegal) {
            fprintf(stderr, "ConvertUTF16toUTF32 illegal seq 0x%04x,%04x\n", ch, ch2);
            fflush(stderr);
        }

#endif
        return result;
    }

    /* --------------------------------------------------------------------- */

    /*
     * Index into the table below with the first byte of a UTF-8 sequence to
     * get the number of trailing bytes that are supposed to follow it.
     * Note that *legal* UTF-8 values can't have 4 or 5-bytes. The table is
     * left as-is for anyone who may want to do such conversion, which was
     * allowed in earlier algorithms.
     */
    static const char trailingBytesForUTF8[256] = {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5
    };

    /*
     * Magic values subtracted from a buffer value during UTF8 conversion.
     * This table contains as many values as there might be trailing bytes
     * in a UTF-8 sequence.
     */
    static const UTF32 offsetsFromUTF8[6] = { 0x00000000UL, 0x00003080UL, 0x000E2080UL,
                                              0x03C82080UL, 0xFA082080UL, 0x82082080UL
                                            };

    /*
     * Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
     * into the first byte, depending on how many bytes follow.  There are
     * as many entries in this table as there are UTF-8 sequence types.
     * (I.e., one byte sequence, two byte... etc.). Remember that sequencs
     * for *legal* UTF-8 will be 4 or fewer bytes total.
     */
    static const UTF8 firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };

    /* --------------------------------------------------------------------- */

    /* The interface converts a whole buffer to avoid function-call overhead.
     * Constants have been gathered. Loops & conditionals have been removed as
     * much as possible for efficiency, in favor of drop-through switches.
     * (See "Note A" at the bottom of the file for equivalent code.)
     * If your compiler supports it, the "isLegalUTF8" call can be turned
     * into an inline function.
     */

    /* --------------------------------------------------------------------- */

    ConversionResult ConvertUTF16toUTF8(
        const UTF16** sourceStart, const UTF16* sourceEnd,
        UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags) {
        ConversionResult result = conversionOK;
        const UTF16* source = *sourceStart;
        UTF8* target = *targetStart;

        while (source < sourceEnd) {
            UTF32 ch;
            unsigned short bytesToWrite = 0;
            const UTF32 byteMask = 0xBF;
            const UTF32 byteMark = 0x80;
            const UTF16* oldSource = source; /* In case we have to back up because of target overflow. */
            ch = *source++;

            /* If we have a surrogate pair, convert to UTF32 first. */
            if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END) {
                /* If the 16 bits following the high surrogate are in the source buffer... */
                if (source < sourceEnd) {
                    UTF32 ch2 = *source;

                    /* If it's a low surrogate, convert to UTF32. */
                    if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END) {
                        ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
                             + (ch2 - UNI_SUR_LOW_START) + halfBase;
                        ++source;

                    } else if (flags == strictConversion) { /* it's an unpaired high surrogate */
                        --source; /* return to the illegal value itself */
                        result = sourceIllegal;
                        break;
                    }
                } else { /* We don't have the 16 bits following the high surrogate. */
                    --source; /* return to the high surrogate */
                    result = sourceExhausted;
                    break;
                }
            } else if (flags == strictConversion) {
                /* UTF-16 surrogate values are illegal in UTF-32 */
                if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END) {
                    --source; /* return to the illegal value itself */
                    result = sourceIllegal;
                    break;
                }
            }

            /* Figure out how many bytes the result will require */
            if (ch < (UTF32)0x80) {
                bytesToWrite = 1;

            } else if (ch < (UTF32)0x800) {
                bytesToWrite = 2;

            } else if (ch < (UTF32)0x10000) {
                bytesToWrite = 3;

            } else if (ch < (UTF32)0x110000) {
                bytesToWrite = 4;

            } else {
                bytesToWrite = 3;
                ch = UNI_REPLACEMENT_CHAR;
            }

            target += bytesToWrite;

            if (target > targetEnd) {
                source = oldSource; /* Back up source pointer! */
                target -= bytesToWrite;
                result = targetExhausted;
                break;
            }

            switch (bytesToWrite) { /* note: everything falls through. */
                case 4:
                    *--target = (UTF8)((ch | byteMark) & byteMask);
                    ch >>= 6;

                case 3:
                    *--target = (UTF8)((ch | byteMark) & byteMask);
                    ch >>= 6;

                case 2:
                    *--target = (UTF8)((ch | byteMark) & byteMask);
                    ch >>= 6;

                case 1:
                    *--target = (UTF8)(ch | firstByteMark[bytesToWrite]);
            }

            target += bytesToWrite;
        }

        *sourceStart = source;
        *targetStart = target;
        return result;
    }

    /* --------------------------------------------------------------------- */

    /*
     * Utility routine to tell whether a sequence of bytes is legal UTF-8.
     * This must be called with the length pre-determined by the first byte.
     * If not calling this from ConvertUTF8to*, then the length can be set by:
     *  length = trailingBytesForUTF8[*source]+1;
     * and the sequence is illegal right away if there aren't that many bytes
     * available.
     * If presented with a length > 4, this returns false.  The Unicode
     * definition of UTF-8 goes up to 4-byte sequences.
     */

    static UTFBoolean isLegalUTF8(const UTF8* source, int length) {
        UTF8 a;
        const UTF8* srcptr = source + length;

        switch (length) {
            default:
                return false;

                /* Everything else falls through when "true"... */
            case 4:
                if ((a = (*--srcptr)) < 0x80 || a > 0xBF) {
                    return false;
                }

            case 3:
                if ((a = (*--srcptr)) < 0x80 || a > 0xBF) {
                    return false;
                }

            case 2:
                if ((a = (*--srcptr)) > 0xBF) {
                    return false;
                }

                switch (*source) {
                        /* no fall-through in this inner switch */
                    case 0xE0:
                        if (a < 0xA0) {
                            return false;
                        }

                        break;

                    case 0xED:
                        if (a > 0x9F) {
                            return false;
                        }

                        break;

                    case 0xF0:
                        if (a < 0x90) {
                            return false;
                        }

                        break;

                    case 0xF4:
                        if (a > 0x8F) {
                            return false;
                        }

                        break;

                    default:
                        if (a < 0x80) {
                            return false;
                        }
                }

            case 1:
                if (*source >= 0x80 && *source < 0xC2) {
                    return false;
                }
        }

        if (*source > 0xF4) {
            return false;
        }

        return true;
    }

    /* --------------------------------------------------------------------- */

    /*
     * Exported function to return whether a UTF-8 sequence is legal or not.
     * This is not used here; it's just exported.
     */
    UTFBoolean isLegalUTF8Sequence(const UTF8* source, const UTF8* sourceEnd) {
        int length = trailingBytesForUTF8[*source] + 1;

        if (source + length > sourceEnd) {
            return false;
        }

        return isLegalUTF8(source, length);
    }

    /* --------------------------------------------------------------------- */

    ConversionResult ConvertUTF8toUTF16(
        const UTF8** sourceStart, const UTF8* sourceEnd,
        UTF16** targetStart, UTF16* targetEnd, ConversionFlags flags) {
        ConversionResult result = conversionOK;
        const UTF8* source = *sourceStart;
        UTF16* target = *targetStart;

        while (source < sourceEnd) {
            UTF32 ch = 0;
            unsigned short extraBytesToRead = trailingBytesForUTF8[*source];

            if (source + extraBytesToRead >= sourceEnd) {
                result = sourceExhausted;
                break;
            }

            /* Do this check whether lenient or strict */
            if (!isLegalUTF8(source, extraBytesToRead + 1)) {
                result = sourceIllegal;
                break;
            }

            /*
             * The cases all fall through. See "Note A" below.
             */
            switch (extraBytesToRead) {
                case 5:
                    ch += *source++;
                    ch <<= 6; /* remember, illegal UTF-8 */

                case 4:
                    ch += *source++;
                    ch <<= 6; /* remember, illegal UTF-8 */

                case 3:
                    ch += *source++;
                    ch <<= 6;

                case 2:
                    ch += *source++;
                    ch <<= 6;

                case 1:
                    ch += *source++;
                    ch <<= 6;

                case 0:
                    ch += *source++;
            }

            ch -= offsetsFromUTF8[extraBytesToRead];

            if (target >= targetEnd) {
                source -= (extraBytesToRead + 1); /* Back up source pointer! */
                result = targetExhausted;
                break;
            }

            if (ch <= UNI_MAX_BMP) { /* Target is a character <= 0xFFFF */
                /* UTF-16 surrogate values are illegal in UTF-32 */
                if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                    if (flags == strictConversion) {
                        source -= (extraBytesToRead + 1); /* return to the illegal value itself */
                        result = sourceIllegal;
                        break;

                    } else {
                        *target++ = UNI_REPLACEMENT_CHAR;
                    }
                } else {
                    *target++ = (UTF16)ch; /* normal case */
                }
            } else if (ch > UNI_MAX_UTF16) {
                if (flags == strictConversion) {
                    result = sourceIllegal;
                    source -= (extraBytesToRead + 1); /* return to the start */
                    break; /* Bail out; shouldn't continue */

                } else {
                    *target++ = UNI_REPLACEMENT_CHAR;
                }
            } else {
                /* target is a character in range 0xFFFF - 0x10FFFF. */
                if (target + 1 >= targetEnd) {
                    source -= (extraBytesToRead + 1); /* Back up source pointer! */
                    result = targetExhausted;
                    break;
                }

                ch -= halfBase;
                *target++ = (UTF16)((ch >> halfShift) + UNI_SUR_HIGH_START);
                *target++ = (UTF16)((ch & halfMask) + UNI_SUR_LOW_START);
            }
        }

        *sourceStart = source;
        *targetStart = target;
        return result;
    }

    /* --------------------------------------------------------------------- */

    ConversionResult ConvertUTF32toUTF8(
        const UTF32** sourceStart, const UTF32* sourceEnd,
        UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags) {
        ConversionResult result = conversionOK;
        const UTF32* source = *sourceStart;
        UTF8* target = *targetStart;

        while (source < sourceEnd) {
            UTF32 ch;
            unsigned short bytesToWrite = 0;
            const UTF32 byteMask = 0xBF;
            const UTF32 byteMark = 0x80;
            ch = *source++;

            if (flags == strictConversion) {
                /* UTF-16 surrogate values are illegal in UTF-32 */
                if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                    --source; /* return to the illegal value itself */
                    result = sourceIllegal;
                    break;
                }
            }

            /*
             * Figure out how many bytes the result will require. Turn any
             * illegally large UTF32 things (> Plane 17) into replacement chars.
             */
            if (ch < (UTF32)0x80) {
                bytesToWrite = 1;

            } else if (ch < (UTF32)0x800) {
                bytesToWrite = 2;

            } else if (ch < (UTF32)0x10000) {
                bytesToWrite = 3;

            } else if (ch <= UNI_MAX_LEGAL_UTF32) {
                bytesToWrite = 4;

            } else {
                bytesToWrite = 3;
                ch = UNI_REPLACEMENT_CHAR;
                result = sourceIllegal;
            }

            target += bytesToWrite;

            if (target > targetEnd) {
                --source; /* Back up source pointer! */
                target -= bytesToWrite;
                result = targetExhausted;
                break;
            }

            switch (bytesToWrite) { /* note: everything falls through. */
                case 4:
                    *--target = (UTF8)((ch | byteMark) & byteMask);
                    ch >>= 6;

                case 3:
                    *--target = (UTF8)((ch | byteMark) & byteMask);
                    ch >>= 6;

                case 2:
                    *--target = (UTF8)((ch | byteMark) & byteMask);
                    ch >>= 6;

                case 1:
                    *--target = (UTF8)(ch | firstByteMark[bytesToWrite]);
            }

            target += bytesToWrite;
        }

        *sourceStart = source;
        *targetStart = target;
        return result;
    }

    /* --------------------------------------------------------------------- */

    ConversionResult ConvertUTF8toUTF32(
        const UTF8** sourceStart, const UTF8* sourceEnd,
        UTF32** targetStart, UTF32* targetEnd, ConversionFlags flags) {
        ConversionResult result = conversionOK;
        const UTF8* source = *sourceStart;
        UTF32* target = *targetStart;

        while (source < sourceEnd) {
            UTF32 ch = 0;
            unsigned short extraBytesToRead = trailingBytesForUTF8[*source];

            if (source + extraBytesToRead >= sourceEnd) {
                result = sourceExhausted;
                break;
            }

            /* Do this check whether lenient or strict */
            if (!isLegalUTF8(source, extraBytesToRead + 1)) {
                result = sourceIllegal;
                break;
            }

            /*
             * The cases all fall through. See "Note A" below.
             */
            switch (extraBytesToRead) {
                case 5:
                    ch += *source++;
                    ch <<= 6;

                case 4:
                    ch += *source++;
                    ch <<= 6;

                case 3:
                    ch += *source++;
                    ch <<= 6;

                case 2:
                    ch += *source++;
                    ch <<= 6;

                case 1:
                    ch += *source++;
                    ch <<= 6;

                case 0:
                    ch += *source++;
            }

            ch -= offsetsFromUTF8[extraBytesToRead];

            if (target >= targetEnd) {
                source -= (extraBytesToRead + 1); /* Back up the source pointer! */
                result = targetExhausted;
                break;
            }

            if (ch <= UNI_MAX_LEGAL_UTF32) {
                /*
                 * UTF-16 surrogate values are illegal in UTF-32, and anything
                 * over Plane 17 (> 0x10FFFF) is illegal.
                 */
                if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
                    if (flags == strictConversion) {
                        source -= (extraBytesToRead + 1); /* return to the illegal value itself */
                        result = sourceIllegal;
                        break;

                    } else {
                        *target++ = UNI_REPLACEMENT_CHAR;
                    }
                } else {
                    *target++ = ch;
                }
            } else { /* i.e., ch > UNI_MAX_LEGAL_UTF32 */
                result = sourceIllegal;
                *target++ = UNI_REPLACEMENT_CHAR;
            }
        }

        *sourceStart = source;
        *targetStart = target;
        return result;
    }
}//namespace behaviac

/* ---------------------------------------------------------------------

	Note A.
	The fall-through switches in UTF-8 reading code save a
	temp variable, some decrements & conditionals.  The switches
	are equivalent to the following loop:
	{
	int tmpBytesToRead = extraBytesToRead+1;
	do {
	ch += *source++;
	--tmpBytesToRead;
	if (tmpBytesToRead) ch <<= 6;
	} while (tmpBytesToRead > 0);
	}
	In UTF-8 writing code, the switches on "bytesToWrite" are
	similarly unrolled loops.

	--------------------------------------------------------------------- */
